In recent years there has been an increasing demand for miniaturization of dielectric elements and improved reliability as electronic circuits reach higher densities, and electronic components such as laminated ceramic capacitors are rapidly becoming more compact, achieving higher capacity, and becoming more reliable while the applications thereof are also expanding. As these applications expand, various characteristics are required, such as temperature characteristics of capacitance in a laminated ceramic capacitor, effective capacitance during application of a DC electric field and reliability.
In order to respond to requirements such as those mentioned above, various types of dielectric compositions comprising BaTiO3 (which has a high dielectric constant) as the main component have been investigated as dielectric compositions which are employed in ceramic capacitors. Among these, it is known that dielectric compositions having an auxiliary component diffused in the surface region of BaTiO3 particles, referred to as dielectric compositions having a “core-shell” structure, can improve characteristics such as the temperature characteristics of dielectric constant, by controlling the composition and range of the shell portion which constitutes the auxiliary component diffusion phase.
For example, a laminated ceramic capacitor having the abovementioned features is described in Japanese Patent Application JP 2000-58377 A.
The laminated ceramic capacitor described in Japanese Patent Application JP 2000-58377 A has a main component in a dielectric ceramic layer represented by the following compositional formula: {Ba1-xCaxO}mTiO2+αRe2O3+βMgO+γMnO (where Re2O3 is at least one selected from among Y2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3 and Yb2O3; α, β and γ express molar ratios such that 0.001≤α≤0.10, 0.001≤β≤0.12 and 0.001<γ≤0.12; and 1.000<m≤1.035 and 0.005<x≤0.22). The content of alkali metal oxide in the {Ba1-xCaxO}mTiO2 starting material used in the dielectric ceramic layer is no greater than 0.02 wt %.
The composition contains 0.2-5.0 parts by weight of either a first auxiliary component or a second auxiliary component with respect to boo parts by weight of the main component. The first auxiliary component is an oxide of Li2O—(Si,Ti)O2-MO (where MO is at least one selected from Al2O3 and ZrO2). The second auxiliary component is an oxide of SiO2—TiO2—XO (where XO is at least one selected from among BaO, CaO, SrO, MgO, ZnO and MnO).
An internal electrode of the laminated ceramic capacitor described in Japanese Patent Application JP 2000-58377 A further comprises nickel or a nickel alloy.
The laminated ceramic capacitor described in Japanese Patent Application JP 2000-58377 A has a core-shell structure in which an auxiliary component is diffused in the region of the grain boundary, and has a core portion in which some of the BaTiO3 constituting the main component of the dielectric ceramic layer is substituted with CaTiO3, and as a result it is possible to restrict a reduction in the dielectric constant when a DC bias is applied and to adequately increase resistivity when a DC bias is applied.
However, in the laminated ceramic capacitor described in Japanese Patent Application JP 2000-58377 A, BaTiO3 constituting the main component occupies the majority of the core portion, so a DC bias is unevenly applied. The dielectric constant of the laminated ceramic capacitor and the DC bias resistivity decrease when a DC bias of 5 kV/mm or greater is applied because the DC bias is unevenly applied.